1. Field of the Invention
The present invention relates generally to battery cell monitoring and, in one possible embodiment, to a lightweight monitoring network with minimal connections that may be utilized to monitor the health of individual battery cells in multi-cell batteries and/or groups of battery cells.
2. Description of Related Art
High voltage batteries may involve connections of many cells or cell modules. Examples of high voltage batteries include battery cell arrays for hybrid cars, aerospace/spacecraft applications, telecommunication power supplies, computer power supplies, uninterruptible power supplies, electric utility energy storage, commercial applications, and the like. High voltage batteries may be of different types including lithium-ion cells, fuel cells, other electrochemical cells, and the like.
In prior art systems, some of which are discussed hereinafter, cell monitoring and/or balancing are achieved either by including complex electronic circuitry at each cell, or electrical connectors with many contacts to allow external circuitry to monitor and balance the cells. Complicated circuitry at each cell is inherently less reliable. If many connections are required, the connectors present electrical shock safety issues. If the connectors are heavy, then they may be unsuitable for aerospace/spacecraft applications.
For some applications, it may be desirable to provide separate battery system components such as an external charger and an external cell charge measurement subsystem. To provide the capability to monitor individual battery cells, a multi-pin connector on the battery is then required. In large high voltage batteries, such a connector has several disadvantages. The connector needs at least one pin per cell. Because the battery can produce high voltages, the sense lines need a safety disconnect or electrical isolation to avoid exposing ground personnel or crew to high voltages when the connector is used. As well, because the battery can produce high currents, the sense lines may also need some sort of fusing or other wire protection as well.
Batteries may utilize different numbers of individual cells depending on the requirements of the system. For example, batteries may have a few cells, thirty or more cells, over one hundred cells, or more. Thus, the number of connections necessary to provide access to individual cells may be quite large.
The following patents show prior art efforts regarding the above and other problems:
U.S. Pat. No. 7,489,048, issued Feb. 10, 2009, to King et al, discloses a battery load leveling system for an electrically powered system in which a battery is subject to intermittent high current loading, the system including a first battery, a second battery, and a load coupled to the batteries. The system includes a passive storage device, a unidirectional conducting apparatus coupled in series electrical circuit with the passive storage device and poled to conduct current from the passive storage device to the load, a series electrical circuit coupled in parallel with the battery such that the passive storage device provides current to the load when the battery terminal voltage is less than voltage on the passive storage device, and a battery switching circuit that connects the first and second batteries in either a lower voltage parallel arrangement or a higher voltage series arrangement.
U.S. Pat. No. 7,425,832, issued Sep. 16, 2008, to Gopal et al, discloses a method and system for measuring impedance and voltage characteristics of individual cells of multi-cell electrochemical devices, for example a battery or a fuel cell stack. The electrochemical system comprises a plurality of cells; a measuring device including a plurality of inputs connected across the plurality of cells to generate voltage and current signals indicative of voltage and current characteristics of the plurality of cells; a current supply/draw means for superimposing modulated current values through the plurality of cells; and a controller for controlling at least one system operating condition based on the voltage and current characteristics received from the measuring device, the controller being connected to the measuring device. The method comprises (a) superimposing modulated current values across a plurality of cells of the electrochemical device; (b) drawing current from the plurality of cells to generate voltage and current signals indicative of voltage and current characteristics of the plurality of cells; and, (c) controlling the at least one system operating condition based on the voltage and current characteristics of the plurality of cells, wherein the at least one system operating condition comprises at least one of temperature, humidity and reactant flow rates, within the electrochemical system.
U.S. Pat. No. 7,315,169, issued Jan. 1, 2008, to Fenske et al, discloses a fault indicator for indicating the occurrence of a fault in an electrical conductor that has a housing, a high capacity battery, at least one light emitting diode (LED) visible from the exterior of the fault indicator upon the occurrence of a fault, which may be automatically reset to a non-fault indicating position a predetermined time after the occurrence of the fault, and electronic circuitry for sensing a fault, for actuating the LEDs to indicate a fault and for resetting the LEDs to a non-fault indicating condition a predetermined time after the fault has occurred. The electronic circuitry conserves energy by drawing insubstantial current from the high capacity battery during non-fault conditions. The electronic circuitry may also include in-rush restraint to avoid false tripping of the fault indicator during surges. An inrush restraint circuit has an output signal that is logically combined with a fault indicator signal to disable the fault indicator during inrush conditions. An improved electrostatic sensor senses the electromagnetic field associated with a monitored conductor, provides less susceptibility to affects from adjacent conductors and provides operating power to the inrush restraint circuitry.
U.S. Pat. No. 6,963,197, issued Nov. 8, 2005, to Feight et al, discloses a fault indicator for indicating the occurrence of a fault in an electrical conductor that is reset at a predetermined time after the fault is detected, such as about 4 hours. The fault indicator has a housing, a high capacity battery, a fault sensor, a display for indicating a fault condition, and a programmable controller with a sleep state that draws low quiescent current. As a result, the battery is expected to last the lifetime of the fault indicator. The fault indicator may optionally include current inrush restraint and/or voltage inrush restraint to inhibit the controller from activating the display to the fault indicating condition during the inrush conditions. The electromagnetic field about the conductor causes an electrostatic sensor to develop a differential voltage signal between two electrodes of different areas for the voltage in rush restraint circuit. Auxiliary contacts are provided to remotely monitor the fault indicator.
U.S. Pat. No. 6,915,220, issued Jul. 5, 2005, to Cardinal et al, discloses an integrated battery monitoring device that includes a pair of input leads for coupling across the terminals of a battery cell to be monitored and a sensor for sensing a desired battery cell parameter. A self-contained power supply has the voltage across the battery cell terminals as an input thereto, the self-contained power supply being configured for providing power to the sensor. A pair of output leads communicates data generated by the sensor.
U.S. Pat. No. 6,844,799, issued Jan. 18, 2005, to Attarian et al, discloses a current sensor and current transformer for monitoring electrical current with a magnetic core having a mixture of magnetic materials to provide a low cost design in a compact configuration with an expanded dynamic range. The mixed material core can be fabricated either from stamped laminations or from coil stock and may include an air gap for activating a magnetic flux sensor. Multiple core configurations are disclosed.
U.S. Pat. No. 6,711,512, issued Mar. 23, 2004, to Noh, discloses a pole transformer load monitoring system using a wireless Internet network. The load monitoring system is capable of measuring, in real time, a variety of load parameters (phase voltages, phase currents and temperatures) of a pole transformer placed on a distribution line. The results of the measurements are transferred to an operator in a branch operating station over the wireless Internet network so as to prevent fosses resulting from overloaded and unbalanced states.
U.S. Pat. No. 6,133,724, issued Oct. 17, 2000, to Schweitzer, Jr. et al, discloses a fault indicator contained within a protective equipment closure of the type used to house pad-mounted components of a power distribution system detects the occurrence of a fault current in a monitored conductor and provides a light indication thereof. The fault indicator includes a circuit monitoring module, having an integral fault indicator flag module, and a remote fault indicator light module. A status-indicating flag is rotatably mounted in the integral fault indicator flag module. The flag is positioned in either a reset indicating position or a fault indicating position by a magnetic pole piece, which is magnetized in one magnetic direction or the other by momentary application of a current in one direction or the other to an actuator winding on the pole piece. A magnetically actuated reed switch in an auxiliary magnetic circuit comprising an auxiliary pole piece magnetized by the actuator winding and a bias magnet magnetically aligned to oppose the reset magnetic orientation and reinforce the trip magnetic orientation of the magnetic pole piece closes upon occurrence of the fault current to connect an internal battery to an LED contained within the remote fault indicator light module so that the LED is visible from the exterior of the protective equipment enclosure. The light indication of the fault occurrence may be reset automatically by a timed reset circuit or manually by a manual reset circuit.
U.S. Pat. No. 6,018,239, issued Jan. 25, 2000, to Berkcan et al, discloses a self-powered axial current sensor for generating a signal which represents current in a power line includes, in one embodiment, a housing having a bus bar opening of substantially rectangular shape extending longitudinally therethrough. The housing also includes current sensor core retaining walls which define a current sensor region, and a cover base wall which defines, with one of the retaining walls, a power core region. A current sensor core and coil are located in the current sensor region and are positioned proximate the bus bar opening. The current sensor core and coil also are substantially symmetrical with respect to the center axis of the bus bar opening. The current sensor further includes a power core and a power coil located in the power core region and positioned substantially symmetrically with respect to the center axis of bus bar opening.
U.S. Pat. No. 6,002,260, issued Dec. 14, 1999, to Lau et al, discloses a fault sensor suitable for use in a heterogeneous power distribution system that executes a stored program and causes sufficient information to be collected to distinguish a source of fault current as being from a public utility portion of the power distribution network or from a distributed generator. Short circuit current and magnetizing current are distinguished based on differences in VI “signatures.” In addition, the fault sensor periodically senses a condition of a battery of the fault sensor. When the condition of the battery indicates the battery power is low, the fault sensor sends a digital data signal including a low battery indication to a remote location. Subsequent to occurrence of a sustained power outage, the sensor detects that power has been restored and sends to a remote location a digital data signal including an indication that power has been restored. The sensor periodically measures peak line voltage and peak line current and reports peak values to the remote location.
U.S. Pat. No. 5,969,625, issued Oct. 19, 1999, to Russo, discloses the method and the apparatus for detecting a deteriorating condition in a bank of standby batteries includes injecting an audio frequency current into one of the battery buses or cables, detecting an audio frequency current signal, matched to the injected audio frequency current signal, that is carried by the battery bus and detecting a voltage drop, at the audio frequency, across the bank of standby batteries. In one embodiment, current transformers are utilized in connection with an oscillator (to inject the AF current signal) and detection circuits (comparators and operational amplifiers) are utilized to generate a representative current signal and a representative voltage signal. The device detects when the standby batteries are operating in a normal, stable condition, that is, when the bank is neither being recharged nor is discharging DC power to the load. During normal, stable operating conditions, a differential relationship is established between the representative voltage and representative current signals. In one embodiment, a microprocessor-based system monitors the float voltage of the battery in order to ascertain when the battery system is in a normal, stable operating condition. The microprocessor also initially establishes the differential between the representative voltage and the representative current signals. The method includes determining when the differential relationship between the voltage and current signals exceeds a predetermined value and issues an alarm signal at that time. The alarm signal may be deferred until the differential relationship exceeds the predetermined value for a predetermined period of time. In one embodiment, this analysis is conducted in the microprocessor-based system.
U.S. Pat. No. 5,923,148, issued Jul. 13, 1999, to Sideris et al, discloses an on-line battery monitoring system for monitoring a plurality of battery cells identifies and computes individual cell and battery bank operating parameters. The system comprises a controller for designating a given battery cell to be monitored, a multiplexer responsive to designation by the controller for selecting a given battery cell to be monitored or for selecting a battery pack to be monitored, an analog board for receiving electrical signals from a given battery cell for providing an output representing measurement of a parameter (voltage, temperature, and the like) of the given battery cell, a voltage sensor circuit for sensing voltage appearing across positive and negative terminals of the battery pack, and a control board responsive to address information for selectively initiating a load test, battery bank charging, or common-mode voltage measurement.
U.S. Pat. No. 5,839,093, issued Nov. 17, 1998, to Novosel et al, discloses both fault location and fault resistance of a fault that are calculated by the present method and system. The method and system takes into account the effects of fault resistance and load flow, thereby calculating fault resistance by taking into consideration the current flowing through the distribution network as well as the effect of fault impedance. A direct method calculates fault location and fault resistance directly while an iterative fashion method utilizes simpler calculations in an iterative fashion which first assumes that the phase angle of the current distribution factor is zero, calculates an estimate of fault location utilizing this assumption, and then iteratively calculates a new value of the phase angle of the current distribution factor and fault location until a fault location is ascertained. Fault resistance is then calculated based upon the calculated fault location. The techniques are equally applicable to a three-phase system once fault type is identified.
U.S. Pat. No. 5,659,237, issued Aug. 19, 1997, to Divan et al, discloses a technique for charge equalization of a series connected string of battery cells. The secondary windings of a transformer having a single primary winding and multiple secondary windings are connected across each battery cell to be equalized. A single power converter applies a charging signal to the primary of the transformer, inducing a charging current in each secondary which is inversely related to the charge on the battery cells to be equalized. The transformer is preferably implemented as a coaxial winding transformer having low secondary-to-secondary winding coupling. The power converter is preferably implemented as a forward converter supplied with DC power from an adjustable DC power source. A source voltage provided by the DC source may preferably be adjusted during the course of charge equalization to preferentially direct charge to weaker cells. The charge equalization system may be used in combination with a bulk charging system to provide for both rapid charging of a battery string as well as equalization of the battery cells within the string.
U.S. Pat. No. 5,656,931, issued Aug. 12, 1997, to Lau et al, discloses a fault current sensor device that detects and distinguishes abnormal current events on alternating current overhead and underground power transmission lines. The sensor distinguishes whether the momentary or sustained fault is a line-to-ground fault, line-to-line fault or a three-phase fault. The sensor determines whether the overload has occurred on all three phases, or only on one or two phases, of the power line in an unbalanced situation. The device can be remotely reprogrammed to alter its trigger or threshold level and can be remotely reset after a fault has occurred.
U.S. Pat. No. 5,390,064, issued Feb. 14, 1995, to Russo, discloses a current limiting method and apparatus for preventing fault overload in a utility power transmission system employs a high power, superconducting coil based pulse transformer for saturating the core of the utility power transformer thereby limiting its current carrying capacity. The utility transformer core is biased to a disadvantageous portion of its B-H curve. A fault condition is detected and as a result, the superconducting coil is quenched thereby sending a high energy pulse of current into the utility transformer magnetic core. The core, while heating, does not exceed its capability to maintain a stable thermal condition while at the same time limiting the current being transformed from its input to output lines, until a transformer circuit breaker activates.
U.S. Pat. No. 5,254,930, issued Oct. 19, 1993, to Daly, discloses a battery charger for charging a plurality of batteries that includes a voltage supply connected by a pair of switches to a power converter including a transformer having a primary winding and a plurality of secondary windings. Each secondary winding is coupled to a battery. Voltage is transferred from the voltage supply to the primary winding when the switches are closed and current is transferred from the secondary windings to the batteries when the switches are open. Charge control circuitry monitors the voltage of each battery and the total battery voltage and determines the amount of current to supply to the batteries. Supervisory logic monitors the current received from the secondary windings by each of the batteries and the voltage of each of the batteries to determine the charge status of each battery and the operating status of the power converter. If one battery continues drawing a greater proportion of the maximum current relative to the remaining batteries after the predetermined voltage limit has been reached, this indicates that there is a short circuited cell causing one battery to draw a greater proportion of current or that there is a cell with high impedance causing one battery to draw a smaller proportion of current. For both fault conditions, the supervisory circuit detects the current imbalance and generates a shutdown signal. The shutdown signal is also asserted when the supervisory circuit detects an over voltage condition in any of the batteries, or an over current in the primary winding. The shutdown signal subsequently precludes further operation of the charge control circuit for a predetermined time period, alerting the system operator of a problem within the battery backup system.
U.S. Pat. No. 4,956,739, issued Sep. 11, 1990, to Becker et al, discloses a device to locate internal faults in a high-voltage capacitor battery that has a plurality of symmetrically parallel and series-coupled capacitor banks arranged in parallel branches coupled by shunt branches. The phase angles of the shunt currents flowing in the shunt branches relative to the total current flowing in the parallel branches are determined. A fault is located in one of the capacitor banks based upon these determined phase angles.
U.S. Pat. No. 4,697,134, issued Sep. 29, 1987, to Burkum et al, discloses a testing device that measures the impedance of secondary cells that form a battery, such as a lead acid battery, while the battery is in a float charge condition and connected to an active electrical load. The impedance measurement is made at a frequency selected to be different from those frequencies otherwise present in the charger-load circuit. A first application of the testing device monitors the battery for a change in impedance that can signal a developing defect in one or more individual cells or intercell connections that can prevent the battery from delivering its stored energy to the load. In a second application, the testing device is used to compare the impedance of individual cells and electrical connections to locate faulty components.
U.S. Pat. No. 4,217,645, issued Aug. 12, 1980, to Barry et al, discloses a system for automatically monitoring a plurality of parameters of a plurality of cells in a lead-acid storage battery system. A transponder means responsive to a frequency pattern corresponding to a digital command is located at each cell to be monitored and includes a plurality of sensors which provide analog signals having an amplitude related to the value of the parameters being monitored. In a remote scanner/display means, a microprocessor generates a digital interrogation command (containing a transponder address, sensor selection, and reply duration commands) which is converted to a frequency pattern and coupled to the transponder. In response to the command, the transponder couples the analog signal from the selected sensor to a voltage-controlled oscillator and the output of the oscillator is coupled for the selected reply duration to the scanner/display means where the frequency of the signal is determined under the control of the processor. The information is stored and averaged within the microprocessor and may be displayed upon operator request and an alarm provided if any parameter of any cell exceeds specified limits.
U.S. Pat. No. 7,148,654, issued Dec. 12, 2006, to Burany et al, discloses a system and method for monitoring cell voltages for a plurality of electrochemical cells connected in series forming a cell stack. The method includes dividing the cells into at least two cell groups, measuring the voltage across each cell group and estimating the minimum cell voltage for each group based on the average cell stack voltage and an estimated number of deficient cells in each group. The lowest minimum cell voltage for the entire cell stack is then determined.
U.S. Pat. No. 7,081,737, issued Jul. 25, 2006, to Liu et al, discloses a monitoring circuit for monitoring a voltage level from each of a plurality of battery cells of a battery pack includes an analog to digital converter (ADC) and a processor. The ADC is configured to accept an analog voltage signal from each of the plurality of battery cells and convert each analog voltage signal to a digital signal representative of an accurate voltage level of each battery cell. The processor receives such signals and provides a safety alert signal based on at least one of the signals. The ADC resolution may be adjustable. A balancing circuit provides a balancing signal if at least two of the digital signals indicate a voltage difference between two cells is greater than a battery cell balance threshold. An electronic device including such monitoring and balancing circuits is also provided.
U.S. Pat. No. 6,983,212, issued Jan. 3, 2006, to Burns, discloses a battery management system for control of individual cells in a battery string. The battery management system includes a charger, a voltmeter, a selection circuit and a microprocessor. Under control of the microprocessor, the selection circuit connects each cell of the battery string to the charger and voltmeter. Information relating to battery performance is recorded and analyzed. The analysis depends upon the conditions under which the battery is operating. By monitoring the battery performance under different conditions, problems with individual cells can be determined and corrected.
U.S. Pat. No. 6,844,703, issued Jan. 18, 2005, to Canter, discloses a battery cell balancing system for a battery having a plurality of cells. The system includes a power supply and a plurality of transformer/rectifier circuits electrically coupled to the cells. Preferential charging occurs for a cell with the lowest state of charge. At least one current limiting device is electrically coupled to the transformer/rectifier circuits and the power supply. The current limiting device buffers a source voltage from a reflected voltage of at least one of the plurality of cells).
U.S. Pat. No. 6,803,678, issued Oct. 12, 2004, to Gottlieb et al, discloses a UPS system for providing backup power to a load includes: a power input; multiple batteries; multiple battery housings, each containing one of the batteries, the batteries being coupled in parallel; multiple battery-monitor processors, each monitor being disposed in a respective one of the battery housings and coupled to the corresponding battery; a UPS processor coupled, and configured, to receive monitor data from the plurality of battery-monitor processors; a UPS-processor housing containing the UPS processor and being displaced from the battery housings; and a power output coupled and configured to selectively provide power from one of the power input and the batteries.
U.S. Pat. No. 6,664,762 issued Dec. 16, 2003, to Kutkut, discloses a battery charger for charging high voltage battery strings that includes a DC-to-AC converter, which drives the primary of a transformer having multiple secondaries. Each secondary winding has a corresponding output stage formed of a rectification circuit, output inductor, and output capacitor. The output terminals of the output stages are connectable either in parallel or series. In either configuration, inductor current and capacitor voltage automatically balance among the output stage circuits. A controller normally regulates output terminal voltage by operating in voltage mode, but limits current by operating in a current mode when the average of inductor currents exceeds a specified limit. Reconfiguration from parallel to series, or vice versa, is obtained physical reconnection of the output stage terminals and adjustment of a single voltage feedback scaling factor. Connecting the output stages in series to produce a high voltage output reduces voltage stresses on the rectification circuits and enables use of Schottky diodes to avoid reverse recovery problems.
U.S. Pat. No. 6,583,603, issued Jun. 24, 2003, to Baldwin, discloses an apparatus and method for controllably charging and discharging individual battery cells or groups of battery cells in a string of batteries employed as a back-up power supply. The apparatus includes battery supply modules for at least partially isolating battery strings from the load bus and primary power supply. The partial isolation is effected by a switching network including two controlled switches arranged in parallel to selectively isolate the string of batteries. In certain disclosed embodiments, one of the controlled switches is turned on to connect the string of batteries to the load bus until the other controlled switch closes. The system includes a main power supply that supplies a power bus to a regulator in each battery supply module, which is used for charging the battery string, and a discharge bus to each battery supply module for discharging the batteries.
U.S. Pat. No. 6,268,711 issued Jul. 31, 2001, to Bearfield, discloses a battery manager that provides the ability to switch multiple batteries, battery cells, or other forms of power sources to power external devices individually, in series, and/or in parallel. The device is typically electronic based and consists of voltage level detecting circuits for comparing each power source to a reference voltage, field-effect transistor (FET) control logic for controlling the switching matrix, and a switching matrix which accomplishes the required configuration of power sources to provide an output power source. The invention can be extended with the addition of an output power monitor, DC/DC converter, and control signals that augment internal switching. Depending upon implementation requirements, the battery manager can be in the form of a single integrated circuit.
U.S. Pat. No. 6,181,103 issued Jan. 30, 2001, to Chen, discloses a system converting a smart battery pack into a removable and data accessible (RADA) battery pack and an intelligent power management algorithm embedded in the host computer. The RADA battery pack contains a temperature sensor, a display unit, and a memory (EEPROM). Peripherals mounted on the host computer side contain a control unit, a charging circuit, a load circuit, a voltage divider, a current detector, a temperature control circuit, and a data bus are used to cope with the removal and data access operation for the AICPM system. The removable and data-accessible battery pack utilizes the functions provided by this invention to read, update, and record data about the battery pack, such as number of times used, remaining capacity, usable time, and nominal capacity. It also stores these data in the EEPROM of the RADA battery pack so that when the battery pack is used next time, the AICPM system can read out these data from the EEPROM and use them as the battery pack new information.
U.S. Pat. No. 6,031,354 issued Feb. 29, 2000, to Wiley et al, discloses an on-line battery management and monitoring system and method for monitoring a plurality of battery cells identifies and computes individual cell and battery bank operating parameters. The system comprises a central monitoring station to which a plurality of controllers is connected, each controller having a plurality of battery cells which it monitors. Features of the invention include the following: display of measurement and alarm condition data for each of the battery cells connected to each of the controllers; color-coded display of data for a battery cell, the display color being dependent upon the condition of the battery; performance of data analysis and initiation of necessary maintenance requests; operation of the controllers in an automatic local mode, automatic remote mode, or maintenance mode; provision for periodic calls from the controllers to the central monitoring station; and generation of red alarm calls, yellow alarm calls, downscale alarm calls, and diagnostic calls between the central monitoring station and the controllers.
U.S. Pat. No. 5,982,143, issued Nov. 9, 1999, to Stuart, discloses an electronic battery equalization circuit that equalizes the voltages of a plurality of series connected batteries in a battery pack. The current waveform is in the shape of a ramp for providing zero current switching. The transformer has a primary winding circuit and at least one secondary winding circuit. In one embodiment, each secondary winding circuit is connected to a different pair of batteries. The equalizing current is provided to the lowest voltage batteries in one-half of the battery pack during one-half of the charging cycle. The equalizing current is then provided to the lowest voltage batteries in the other half of the battery pack during the other half of the charging cycle. In another embodiment, each secondary winding circuit is connected to a different single battery. The equalizing current is supplied to a lowest voltage battery in the battery pack during each half of the switching cycle. The electronic battery equalization circuit also includes a feedback control circuit coupled to the primary winding circuit for controlling the current from the equalizing current supply source. In another embodiment, optically coupled switches are connected to a battery voltage monitor to provide equalizing current to the lowest voltage even and odd numbered battery in the battery pack.
U.S. Pat. No. 5,923,148 issued Jul. 13, 1999, to Sideris et al, discloses an on-line battery monitoring system for monitoring a plurality of battery cells identifies and computes individual cell and battery bank operating parameters. The system comprises a controller for designating a given battery cell to be monitored, a multiplexer responsive to designation by the controller for selecting a given battery cell to be monitored or for selecting a battery pack to be monitored, an analog board for receiving electrical signals from a given battery cell for providing an output representing measurement of a parameter (voltage, temperature, and the like) of the given battery cell, a voltage sensor circuit for sensing voltage appearing across positive and negative terminals of the battery pack, and a control board responsive to address information for selectively initiating a load test, battery bank charging, or common-mode voltage measurement.
U.S. Pat. No. 5,914,606 issued Jun. 22, 1999, to Becker-Irvin, discloses a circuit and method for making differential voltage measurements when one or both measurement points are at voltages that exceed those allowed by a typical differential amplifier, and is particular useful for monitoring the individual cell voltages of a number of series-connected cells that make up a rechargeable battery in which some cell voltages must be measured in the presence of a high common mode voltage. Each measurement point is connected to an input of a respective voltage divider, with all the divider outputs connected to a multiplexer having two outputs. The two multiplexer outputs are connected to a differential amplifier. When the voltage dividers are “closely matched,” the output of the differential amplifier is directly proportional to the differential voltage between the pair of points to which the dividers are connected, and the differential voltage between those two points is accurately determined. The voltage dividers divide down the voltage of each measurement point so that each is low enough to be input to a conventional differential amplifier. By selecting the “ratio” of each voltage divider, the circuit can be used to measure differential voltages in the presence of almost any common mode voltage. The invention requires a single differential amplifier powered by a conventional dual power supply.
U.S. Pat. No. 5,666,040, issued Sep. 9, 1997 to Bourbeau, discloses a safe, low-cost battery monitor and control system, Electronic modules are connected to the terminals of respective batteries that make up a series string. Each module produces a go/no-go signal for each of four battery conditions: over-voltage, under-voltage, over-temperature and float-voltage, which are read by a network controller connected to each module via a single three-wire local area network. Based on the information received, the controller can adjust the charging current to the string, terminate the charge cycle, limit the current drawn from the string when in use, or disconnect the string from the system it is powering. The controller can record a history of the charge and discharge activity of each battery, so that the weakest batteries can be identified and replaced instead of scrapping the entire string. The system controls the charging current delivered to each battery during a charge cycle to insure that each battery is neither overcharged nor undercharged, by connecting a bypass circuit across the battery's terminals to reduce the charging current when an over-voltage condition is detected, or by reducing charge current to the string. A battery's voltage measurement is temperature compensated so that it can be accurately compared to temperature dependant limits. The addressable switch is bidirectional, so that the controller can, for example, force bypass resistors to be connected across selected batteries in order to heat up the batteries in a cold environment.
US Patent Publication 2007/0279003, published on Dec. 6, 2007, to Altemose et al, discloses a system for balancing charge between a plurality of storage battery cells within a storage battery. The battery balancing system sense changes, possibly caused by environmental influences, in the overall resonant frequency of charge balancing circuits contained within the battery balancing system. Using a phase locked loop based controller, the battery balancing system compensates for the change in resonant frequency by driving the battery balancing circuits at a frequency that matches the actual sensed resonant frequency of the battery balancing circuits.
An article by Kong Zhi-Guo et al, is entitled “Comparison and Evaluation of Charge Equalization Technique for Series Connected Batteries”, Power Electronics Specialists Conference, 2006. PESC '06. 37th IEEE 18-22 Jun. 2006, pp. 1-6.
An article by Jim Williams and Mark Thoren is entitled “Novel measurements circuit eases battery-stack-cell design”, EON, Jan. 10, 2008, p. 47.
An article by N.H. Kutkut et al, is entitled “Charge equalization for series connected battery strings”, Industry Applications, IEEE Transactions on Volume 31, Issue 3, May-June 1995 pp. 562-568.
The above approaches do not solve the aforementioned problems. According to the inventors, it would be desirable to provide a cell monitoring system with minimal complexity, which also provides features that eliminate the need for fusing on sense lines, provides electrical isolation for each cell, limits leakage current drains on the cells, and limits the overcharge rates for the individual battery cells. It would be desirable to keep the number of connections to a minimum. In battery assemblies, it is often desirable to monitor the cell voltages of the individual cells, strings of cells, and/or the entire battery to improve the battery operation and lifetime. Those of skill in the art will appreciate the present invention that addresses the above and other problems.